PickBestUV: fix VP8Copy16x8 invocation

param order is src, dst

broken in:
66ad372 factorize BPS definition in dsp.h and add VP8Copy16x8

Change-Id: I761f618e3fe31ae7f58953256381f4f16bdb238e
MIPS: fix functions to use generic BPS istead of hardcoded value

Change-Id: I2d68abef886eff7f8df230f155b758dccd7d04fd